The adaptive advantage of an increased hemoglobin-oxygen affinity to tissue oxygenation during hypoxic stress associated with exposure to altitude will be studied. Hemoglobin-oxygen affinity will be selectively altered by administering sodium cyanate. The effects of cyanate treatment on hemoglobin-oxygen affinity and on the general condition of the experimental animals and the effect of selectively increasing hemoglobin-oxygen affinity on oxygen transport on selected acclimation responses to altitude exposure will be examined. The acclimation responses will include the effects of altitude exposure on blood hematocrit ratio, hemoglobin concentration, blood oxygen capacity, blood and plasma volumes, and heart-to-body weight ratios. Whether there is an association between the acclimation response and a concomitant change in capacity for oxygen transport will also be established by quantitatively determining the rate of oxygen consumption, cardiac output and arteriovenous oxygen difference at preselected oxygen tensions. The capacity for oxygen transport will be determined under conditions of rest and exercise at intermediate and high altitudes. The proposed reseach will make it possible to determine the significance of hemoglobin-oxygen affinity to oxygen transport and to the acclimation responses which occur following exposure to the hypoxia of high altitudes. Additional information that will be obtained includes the significance of tissue myoglobin concentrations to oxygen transport at altitude and, the effects of acute and chronic treatment with cyanate, to altitude.